1. Field of the Invention
The present invention relates to a circuit breaker incorporated into an automobile and others.
2. Description of the Related Art
In general, in the electric circuit incorporated into an automobile, it is common to use a fuse or fusible link as a means for quickly shutting off the electric circuit when an overcurrent or a short circuit current flows in the electric circuit. Basically, these fuse and fusible link are composed in such a manner that a fusible conductor is arranged in a case and that a terminal for connection is arranged on the outside of this case. In many cases, these fuse and fusible link are put into practical use being connected with an electric connection box.
However, the above fuse and fusible link are fused for the first time when an overcurrent flows in the electric circuit and the electric circuit is shut off. Therefore, it is impossible to forcibly shut off the electric circuit at an arbitrary time. Accordingly, in case of emergency, for example, when an automobile accident has occurred, it becomes necessary to forcibly shut off an electric circuit for the purpose of safety even if no overcurrent flows in the electric circuit. Therefore, instead of the above fuse and fusible link, or in addition to the above fuse and fusible link, it is necessary to provide a circuit breaker for forcibly shutting off the electric circuit by operation conducted from the outside.
In order to provide the above circuit breaker, as disclosed in Japanese Examined Patent Publication No. 58-47809, it is possible to use a circuit breaker by which a conductor incorporated into the circuit is broken by explosive force of gunpowder. This circuit breaker is composed as follows. An output fuse, gunpowder and filament to heat the gunpowder are enclosed in a single sealed glass case, and an input terminal connected with the filament is led outside the sealed glass case in such a manner that the input terminal penetrates the sealed glass case. A surface of this sealed glass case is covered with an explosion-proof coat.
According to the above circuit breaker, when the input terminal is given an electric current or voltage, the intensity of which is not lower than a predetermined value, and the filament is heated, the gunpowder is exploded by the heat generated in the filament. Therefore, it is possible to forcibly break the conductor by the explosive force. Accordingly, in case of emergency, for example, when an automobile accident has occurred, it is possible to shut off the circuit at any time by controlling an input current or input voltage given to the input terminal.
However, according to the circuit breaker disclosed in the above patent publication, the explosive power of gunpowder is dispersed in the sealed glass case in all directions, and only one portion of the explosive power acts on the output fuse. Therefore, a considerably high intensity of explosive power is required for breaking the fuse positively. However, when the intensity of explosive power is enhanced by increasing a quantity of gunpowder, the inside of the sealed glass case is given a high intensity of explosive force. Therefore, the sealed glass case must have a strong structure so that it can withstand the high intensity of explosive power. Further the sealed glass case must be made of expensive material or it must be subjected to a special treatment for enhancing the mechanical strength. Accordingly, the manufacturing cost is inevitably increased.
On the other hand, a great task to be accomplished is the prevention of dispersion of broken pieces of the inner structure including the conductor.
Further, Japanese Unexamined Patent Publication No. 10-55742 discloses a related circuit breaker. The circuit breaker disclosed in the above patent publication is described as follows. A conductor for composing a circuit is arranged in a case, and an explosion unit for exploding gunpowder is arranged below the conductor. In the case of emergency, the explosion unit is operated, so that the conductor is exploded. Due to the foregoing, the circuit can be quickly and forcibly shut off.
In the above circuit breaker, when the case is tightly shielded up, there is a possibility that the pressure in the case is increased too high by the action of gas generated in the explosion of gunpowder, and further it becomes difficult for the temperature in the case to be lowered. For the above reasons, it is preferable to provide vent holes on the case. However, when the vent holes are provided as described above, not only gas but also flames are dispersed from the vent holes to the outside, which has a bad influence on parts arranged in the peripheral portion. According to the related arrangement, in order to prevent the flames from dispersing from the vent holes to the outside, the case must be covered with a sufficiently large cover, the mechanical strength of which is high, or alternatively the size of the case itself must be increased. Therefore, it is difficult to reduce the overall size and weight of the circuit breaker.